The disclosure of Japanese Patent Application No. HEI 12-037131 filed on Feb. 15, 2000 including the specification, drawings and abstract is incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to a physical quantity detector apparatus which has a vibrator that is displaceably supported on a substrate and which detects a physical quantity, such as angular speed, acceleration, etc., in accordance with the displacement of the vibrator relative to the substrate caused by the force applied to the substrate or the vibrator.
2. Description of the Related Art
Angular speed detector apparatuses as described in Japanese Patent Application Laid-Open No. HEI 10-103960 have been well known. In such an apparatus, a quadrate vibrator is supported onto a substrate so that the vibrator is horizontally displaceable. Using driving electrodes provided on two opposite sides of the quadrate vibrator, the apparatus vibrates the vibrator in the direction of an X-axis that is perpendicular to the two sides of the vibrator. Using detecting electrodes provided on the other two opposite sides of the vibrator, the apparatus detects the angular speed occurring about a vertical axis by detecting vibration of the vibrator in the direction of a Y-axis perpendicular to these two sides. The driving electrodes and the detecting electrodes are respectively made up of a comb-like fixed electrode having a plurality of electrode fingers and a comb-like movable electrode having a plurality of electrode fingers. The electrode fingers of each fixed electrode are fixed to the substrate, and extend from a base portion of the fixed electrode in parallel to one another. The electrode fingers of each movable electrode are provided so as to be displaceable together with the vibrator. The electrode fingers of each movable electrode extend from its base portion in parallel to one another. Voltage is applied between the fixed and movable electrodes. As a result, in the driving electrodes, the electrode fingers of each movable electrode are drawn in a direction of an axis in accordance with the electrostatic attraction that acts between side surfaces of the movable electrode""s electrode fingers and side surfaces of the fixed electrode""s electrode fingers, so that the movable electrode vibrates in the directions of the axis (i.e., the directions of the length of the electrode fingers) relatively to the fixed electrode. In the detecting electrodes, the electrode fingers of each movable electrode are displaced in accordance with the Coriolis force that is proportional to the angular speed (Coriolis force will be explained below). Based on changes in the capacitance between the movable electrode""s electrode fingers and the fixed electrode""s electrode fingers, the angular speed is detected.
However, the above-described conventional apparatus has the following drawback with regard to both the driving and detecting electrodes. That is, as distal end surfaces of the movable electrode""s electrode fingers approach the base portion of the fixed electrode, which face the distal end surfaces of the movable electrode""s electrode fingers, the electrostatic attractions acting between the distal end surfaces of the movable electrode""s electrode fingers and the base portion of the fixed electrode and the electrostatic attractions acting between the distal end surfaces of the fixed electrode""s electrode fingers and the base portion of the movable electrode increase. These electrostatic attractions are forces that are unnecessary for the driving of the movable electrodes of the driving electrodes and for the detection of displacement of the movable electrodes of the detecting electrodes. As these forces increase, the movable electrodes of the driving and detecting electrodes fail to move with high precision as intended. Thus, the conventional angular speed detector apparatus has a problem of degraded detection precision.
Accordingly, it is an object of the invention to contrive so that the electrostatic attraction acting between the aforementioned distal end surfaces and the base portion does not greatly affect either the driving of the movable electrode used in driving electrodes or the detection of displacement of the movable electrode used in detecting electrodes. That is, it is an object of the invention to provide a physical quantity detector apparatus wherein the precision in measuring a physical quantity based on the displacement of the movable electrode is improved by allowing the movable electrode to be displaced with good precision due to the aforementioned contrivance.
In order to achieve the foregoing objects, a construction feature of the invention exists in a physical quantity detector apparatus that has a vibrator displaceably supported to a substrate and that detects a physical quantity in accordance with a displacement of the vibrator, the apparatus including: a comb-like fixed electrode fixed to the substrate and having a plurality of electrode fingers that extend from a basal portion of the fixed electrode in parallel to each other; and a comb-like movable electrode being displaceable together with the vibrator and having a plurality of electrode fingers that extend from a basal portion of the movable electrode in parallel to each other and that are inserted between the electrode fingers of the fixed electrode, wherein as a voltage is applied between the fixed electrode and the movable electrode, the movable electrode is displaced in a direction of an axis of each electrode finger (i.e., a direction of the length of each electrode finger). More specifically, the feature is that a distance D1 from a distal end surface of each electrode finger of the movable electrode to the basal portion of the fixed electrode facing the distal end surface of each electrode finger of the movable electrode, a distance D2 from a distal end surface of each electrode finger of the fixed electrode to the basal portion of the movable electrode facing the distal end surface of each electrode finger of the fixed electrode, a maximum displacement A of the movable electrode in the direction of the axis of each electrode finger, a width w of each electrode finger of the movable electrode and of each electrode finger of the fixed electrode, and a distance d between each electrode finger of the movable electrode and an adjacent electrode finger of the fixed electrode in a direction of the width satisfy a relationship of:
1/(5dw) greater than {1/(D1xe2x88x92A)2}+{1/(D2xe2x88x92A)2}.
In the physical quantity detector apparatus constructed as described above, the aforementioned relationship:
1/(5dw) greater than {1/(D1xe2x88x92A)2}+{1/(D2xe2x88x92A)2}
is a relationship in which the distances D1, D2, d and the width w are set such that the electrostatic attraction that acts between the distal end surfaces of the electrode fingers of the movable electrode and of the electrode fingers of the fixed electrode and the basal portions of the fixed and movable electrodes facing the distal end surfaces has no great effect on the driving of the movable electrode in a case where the fixed and movable electrodes are used as driving electrodes, and has no great effect on the displacement of the movable electrode in a case where the fixed and movable electrodes are used as detecting electrodes. Therefore, the movable electrode can be displaced with good precision. Hence, the precision in measuring a physical quantity by utilizing the displacement of the movable electrode can be improved.